Project Summary Endometriosis is a significant female disease characterized by infertility and pelvic pain in which endometrial stromal and glandular tissue grow in ectopic locations. Several contributing factors such as poor oocyte quality, impaired implantation and progesterone resistance have been implicated as contributing factors to endometriosis-associated infertility, yet the precise mechanisms are poorly understood. Progesterone resistance is thought to influence both the ectopic (endometriotic lesion) and eutopic endometrium. Altered responsiveness of endometriotic lesion tissue is proposed to contribute to the survival of the ectopic tissue, while inability of eutopic endometrium to adequately respond to progesterone is believed to contribute to the infertility associated with the disease. Numerous studies have demonstrated that in women with endometriosis, endometrial progesterone target genes are misexpressed. Several theories on the molecular basis of progesterone resistance in endometriosis have been put forth including altered expression of progesterone receptors (PGR)-A and PGR-B, as well as inflammation, genetics, and epigenetics. However, the exact mechanism of this resistance has yet to be fully elucidated. Thus, there remains a critical gap in our knowledge as to why endometrium (both eutopic and ectopic) from women with endometriosis exhibits altered progesterone responsiveness. Preliminary findings in support of this application suggest that protein expression of the neuron-restrictive silencer factor/RE1-silencing transcription factor, REST is absent/severely reduced in both eutopic and ectopic endometriotic lesion tissue in women with endometriosis. REST is a transcriptional repressor that primarily represses neuronal gene expression in non-neuronal tissues, but can also act as an enhancer of gene transcription and may function in a similar capacity for progesterone action in endometrial tissue. The current study will expand upon our preliminary findings and test the hypothesis that loss of REST expression in eutopic and ectopic endometrium leads to an inability to adequately respond to progesterone, which respectively leads to an inability to produce offspring (infertility) and allows persistence of endometriotic lesion survival. This hypothesis will be tested under two specific aims which will: 1) delineate the REST-progesterone pathway in ectopic and eutopic endometrium and verify the role of REST in regulation of progesterone target genes, and 2) demonstrate functional necessity of REST in regulation of progesterone responsiveness in endometriosis- associated infertility and pain as well as stromal to epithelial cell to cell signaling. Outcomes from this study will provide new insight into the role of REST as a mediator of progesterone action and will lead to identification of novel REST/progesterone targets which may be serve as future therapeutic targets for endometriosis treatment.